Primary or secondary amines can be produced in known manner by catalytic hydrogenation of aldimines or ketimines in the presence of ammonia, generally referred to as aminating hydrogenation. Primary amines are similarly attainable by aminating hydrogenation of nitriles. Suitable hydrogenation catalysts are in particular those based on or more of the metals cobalt, nickel and ruthenium; these catalysts can contain in addition other metals, as a result of the production or as promoters. Increasing the selectivity of the aminating hydrogenation by the presence of an alkali metal hydroxide or alkaline-earth hydroxide is also known.
According to WO 92/21650, dinitriles having high selectivity can be converted into aminonitriles by carrying out the hydrogenation with hydrogen using a Raney nickel or Raney cobalt catalyst in the presence of ammonia and of an organic base, such as LiOH, NaOH or KOH.
The one- or two-step production of isophoronediamine from isophorone nitrile (=3-cyano-3,5,5-trimethylcyclohexanone) is also based on an aminating hydrogenation. In the one-step embodiment, isophorone nitrile is iminated in situ in the presence of ammonia and the isophorone nitrile imine formed is hydrogenated to isophoronediamine--see, for example, EP-A 0 659 734. In the two-step embodiment, in a first step isophorone nitrile is iminated in the presence or absence of an acidic imination catalyst and the reaction mixture containing the isophorone nitrile imine is passed to the hydrogenation step--see, for example, DE-PS 195 40 191, EP-B 0 449 089 and EP-A 0 729 937. As isophoronediamine is a large-scale industrial product, the endeavours of the experts are directed towards obtaining as pure a product as possible in the highest yield possible.
EP-A 0 449 089 discloses a two-step process for the production of isophoronediamine (IPDA) from isophorone nitrile (IPN) wherein, in a first step, IPN is reacted with ammonia on acidic metal oxides to form isophorone nitrile imine and then, in the presence of ammonia and of a hydrogenation catalyst, in particular a catalyst based on cobalt and/or ruthenium, optionally in the presence of basic components such as alkali metal hydroxides or alkaline-earth hydroxides or basic supports, the imine is hydrogenated with hydrogen to form IPDA. In the reworking of the process according to EP-B 0 449 089, in which, however, an organopolysiloxane containing sulfo groups as in DE patent application 196 27 265.3 was used as imination catalyst and the hydrogenation was carried out at 6 MPa instead of at 25 MPa, it was found that with the sole use of a basic cobalt catalyst (90% Co, 5% Mn and 1.9% Na), the yield of isophoronediamine rapidly decreased with increasing operating time--see comparison example 4. It was also ascertained--see comparison examples 5 to 7--that even on continuous addition of an alkali metal hydroxide to the aminating hydrogenation of isophorone nitrile imine, as recommended in EP-A 0 729 937, there is still a considerable formation of secondary products which lead to a decrease in the yield of pure isophoronediamine during the working up of the reaction mixture by distillation.